The invention relates to the membrane separation of methanol from formaldehyde and/or formaldehyde aqueous mixtures. In another aspect the invention relates to hydrophobic polymeric membrane separation of methanol from formaldehyde contained in aqueous mixture feedstreams. Yet in another aspect the invention relates to a process for the hydrophobic, polymeric membrane separation of methanol from formaldehyde and water contained in aqueous mixture feedstreams. Still another aspect of the invention relates to a process for the removal of unreacted methanol contained in formaldehyde streams resulting from the process of manufacturing formaldehyde from methanol.
The separation of organic components from aqueous mixtures such as dispersions, emulsions, solutions, and the like has been accomplished by various means, for example, distillation, filtration, solvent extraction and a combination of these and other methods. However, these methods often fail to provide satisfactory separation of the organic components from the aqueous solution without the utilization of multi-unit apparatus or the high energy input required by phase change techniques. Solvent extraction methods frequently result in the exchange of one aqueous organic mixture for another thus presenting the continuing need for the separation of organic components from aqueous solutions thereof. Because of the disadvantage of the existing method for the separation of organic components from aqueous solutions, and/or mixtures, a simple, inexpensive process adaptable for all types of aqueous solutions is highly desirable.
Membrane separation techniques have been utilized to separate mixtures of two or more molecules, for example, aqueous mixtures, mixed hydrocarbons, azeotropic mixtures, and the like. However known separation techniques utilized in the separation of aqueous mixtures frequently are followed by secondary procedures such as distillation. Because of the disadvantage of the existing separation methods which principally involve a substantial energy input of a thermal, chemical, or mechanical nature, a simple membrane separation for separating methanol from formaldehyde or from formaldehyde aqueous solutions is needed.
The growing need for additional sources of water from salt water or from contaminated sources has directed intensive investigations into the separation of water from aqueous mixtures. Substantial improvements have been made in known water separation procedures based on flash evaporation, membrane separation, electrodialytic action, freezing and the like. However, paralleling such needs for additional sources of water is the need for improved recovery procedures concerning organic components contained in aqueous industrial streams, as well as waste streams. In order to achieve an inexpensive separation of organic components from aqueous mixtures, techniques must be developed which require minimum equipment and energy input.
Accordingly an object of this invention is to provide for the selective separation of methanol from formaldehyde and from formaldehyde aqueous streams utilizing polymeric membrane systems. Another object of this invention is to provide membrane pervaporization, liquid-liquid dialysis, or gas to gas separation of methanol from formaldehyde or from formaldehyde aqueous mixtures wherein the process is as quantitative as possible.